Mutability
by Kelly Chambliss
Summary: Severus thought he'd already imagined every possible order Lord Voldemort could give him. He was wrong. Set at the end of GoF. Snape/McGonagall pairing
1. Chapter 1

A/N - The opening line comes from _Goblet of Fire_. The characters and world, of course, come from JKR. I make no claim to her empire. My grateful thanks to The Real Snape and Moira of the Mountain for their usual expert beta work.

~ / ~ / ~

"If the time should come when you have to make a choice between what is right, and what is easy, remember. . ."

Dumbledore's words filled the Great Hall of Hogwarts, soaring to the enchanted ceiling almost as if they were owls on the wing, and Severus Snape gritted his teeth against the sanctimony of it. "A choice between what was right and what was easy. . ."

As if the wrong choices weren't equally difficult. As if one could even tell what the right and wrong choices were.

Well, grinding his teeth had clearly been a wrong choice: it made the pain in Severus's head pulse like a thing alive. Looking down into the Hall from the staff table, he could see row after row of rapt student faces, eyes fixed on Dumbledore, waiting for the Headmaster to assure them that Cedric Diggory had not died in vain. And to assure them that they themselves were safe and would not die at all.

What little appetite Severus had for the Leaving Feast abruptly left him. Most of the students, even many of his too-often-reviled Snakes, were counting on Dumbledore, counting on him far too much, and suddenly Severus couldn't bear the sight of their yearning faces another minute longer. No one should be asked to look at that level of blind trust - - at least not without retching.

He shifted his head slightly so that he could gaze down the line of staff instead, but they were no easier to watch. There was Hagrid, as usual staring at Dumbledore with dumb adoration. And Moody, so damned jumpy that he could hardly stay in his chair. . . what the hell was the man even doing at table? He should be somewhere quiet where he could recover from spending nine months in a fucking trunk, not sitting here on display, listening to platitudes. He was positively unnatural.

And so was Minerva, seated so quietly to Severus's left. From the corner of his eye, he could see her hands folded unmoving in the lap of her dark robe. She'd stood up, as they all had, when Dumbledore had offered a toast to Diggory, but otherwise she'd been nearly motionless, and since they'd sat down after the toast, Severus didn't think she'd so much as twitched a fingertip.

She'd been unlike herself for a while now, particularly since she'd witnessed the Dementor suck the mind out of Barty Crouch, Junior. In the staffroom, she was atypically quiet, and when she did speak, she was even more waspish than normal. She probably blamed herself - - for the Dementor, for Diggory, for Merlin-knew-what. Severus knew the drill; it was the sort of thing he did himself.

He deliberately turned his back towards her. There were many things Severus didn't need, and one of them was to witness the expression of desperate hope that he was sure he'd find on Minerva's face as she listened to Albus - - because he knew that only years of hard-won self-control enabled him to keep a similar expression off his own face.

He wanted to despise Minerva for her unquestioning faith in a man who seemed to enjoy keeping even his most loyal lieutenants in a state of uncertainty. But he couldn't, not completely.

He couldn't, because despite everything, Severus still had some of the same faith. He still wanted to think that salvation lay in a flamboyant old man who could roll phrases off his tongue with the glibness of the born con artist. He still wanted to shout aloud, the way the other children had done at the Christmas panto his Muggle gran had taken him to see: "We believe! We believe!"

Except that even as a little boy, Severus had not, in the end, been able to open his mouth.

St. Albus, protect us.

Beside him, Minerva still hadn't moved, and when he again caught sight of her folded hands, Severus realised that they were clenched so tightly that the bones seemed about to break through the skin.

~ / ~ / ~

"Wormtail. Severus needs another drink."

Severus didn't need another drink. He hadn't needed or wanted the first drink, either, but one didn't refuse the hospitality of Lord Voldemort. At least the alcohol allowed him to wash away the some of the taste of Dumbledore's speech. Plus, there was the pleasure of being waited upon by an obviously terrified rat of a Peter Pettigrew. The only thing better would be to have Pettigrew replaced by an equally terrified cur of a Sirius Black.

As he poured the firewhisky, the rat-boy's new magical silver hand shook so badly that the heavy decanter chattered against the rim of the glass, and Severus let his lip curl in satisfied derision. Even for a depressive former Death Eater in thrall to two masters, life could sometimes be sweet.

"Leave us, Wormtail," the Dark Lord said, and Severus knew that the real business of the evening was about to begin.

The summons to Voldemort's side had actually come as a relief. After Dumbledore had finally stopped talking and allowed the Leaving Feast to begin, the noise level in the Great Hall had rapidly become appalling, and the pain in Severus's head had just as rapidly become unbearable. For once the sudden burning of the Dark Mark on his arm had been welcome.

A pointed glance at Dumbledore had earned him a quick nod of dismissal, and soon Severus had exchanged the din and stabbing light of the Great Hall for the quiet, cool dimness of the Dark Lord's drawing room, where the fire in the grate was the only illumination, and the only sounds were the crackle of the flames and the oddly soothing slither of Voldemort's great snake as it moved along the wall.

Severus's headache ebbed as the whisky warmed him. No doubt a fresh hell was about to open up before him, but for the moment, he needed to do nothing but take a very occasional sip and listen to what was said to him. He realised that for the first time in weeks, he felt almost calm; he nearly smiled at the notion of what Dumbledore would say if he'd known that an evening with Voldemort could still be preferable to one spent at Hogwarts.

As if he'd heard the thought of his name, the Dark Lord began to speak. "You answered my call promptly, Severus," he said. "You haven't forgotten how the small things please me."

He was at his most genial, focusing his attention on Severus with that single-minded, concerned intensity that had once made an awkward, bitter boy from Spinner's End feel interesting and important.

But Severus, for good or ill, was no longer that boy. "No, I haven't, my lord," he said, his voice as neutral as he could make it - - yet another useful talent honed, ironically, upon the dullness of many of his Hogwarts colleagues. One couldn't fire off sarcasm all the time, no matter how easy the targets. A dry blandness, he'd learnt, could often pass for politeness.

"Do you find me a hard man to please?" Voldemort enquired.

"At times, yes." It was always a gamble, gauging just how much truth the Dark Lord would tolerate, but Severus had become skilled at navigating these waters, especially in the safer harbour at the beginning of a meeting. Later it would be rougher, for Voldemort inevitably became frustrated with what he saw as the stupidity of his minions, and of course, it was still unclear just how much he might have changed after his years of exile.

But all was well for the moment. Voldemort gave a short laugh and leant back in his chair, seemingly at ease. "Ah, you would rather risk my displeasure than lie to me, Severus. I like that. It's a lesson that others could well learn. Had you said 'no,' I would have known you were lying. Of _course_ I am a hard man to please. If the things I wanted were easily accomplished, what would be their value?"

"Indeed."

"Yet I think you might not be unhappy with the task I am going to set you tonight. It's hardly a task, in fact - - think of it as a reward, my friend. Yes, a reward." The Dark Lord sat forward again and looked at Severus intently as he went on, in an apparent non-sequitur that Severus was sure was anything but, "I find myself recalling the days of your unfortunate infatuation with that Mudblood girl."

Voldemort's slits of eyes suddenly narrowed even further, something that in the past had often signaled that he was about to attempt Legilimency. Severus had to fight the instinct to raise his Occlumency shields: the Dark Lord would not be pleased to sense them, and in any case, what Severus needed was not a full barrier but a selective opening of his thoughts. He'd vastly improved his abilities in mental magic since the last time Voldemort had searched his mind, so he didn't fear too deep an intrusion. Still, he'd have to let the Dark Lord see _something_.

Severus forced himself to breathe calmly; he needed only to keep one step ahead of Voldemort's probings, figuring out from the thoughts he touched what he wanted to see. Then it was just a matter of steering him. . .

He felt the first tendrils of Legilimency slide into his mind, the merest brush of mental Devil's Snare. "Do you still pine for the Mudblood?" Voldemort asked softly.

Ah, this one Severus could answer openly. "No, my Lord." It was true: the idea of Lily, the fact of her, was something that had marked him more deeply than the Mark on his arm ever would, but the reality of her had faded. Her memory was now only a bruise, no longer an open wound, and in truth, the only times he could even see Lily clearly were when someone - - Dumbledore, or tonight, Voldemort - - came directly into his mind and brought her back.

He let the Dark Lord touch that mental bruise, feel the mildness of it, and almost at once he could sense the other man's satisfaction.

"Excellent," Voldemort murmured, but then, as if unwilling to offer approbation too quickly, he immediately asked, "yet once you would have said you loved her?"

"I thought I did, yes." It was a confession of sorts, but not a dangerous one. If he had to admit a fault, Severus knew, far better that it be a fault from the past, and one the Dark Lord was already sure of. Besides, when they weren't threatening his current plans, Voldemort always liked to see evidence of his subordinates' weaknesses.

"And what do you say of love now?"

No one in the Dark Lord's service - - well, no thinking person - - would have failed to plan an answer to this question, and Severus, though he sometimes wished he could do _less_ thinking, was ready with his. "Love is something that many people believe in. But to me it is only a word."

He wasn't even lying.

A minute passed, then two, and finally, slowly, he felt Voldemort withdraw from his thoughts, the Dark presence sliding away like greasy rain down a windowpane.

For another moment there was only the crackle of flames in the fireplace. Then Voldemort said, "Many men make mistakes in their youth, Severus. What matters is whether they learn from the experience. Not many do, but you have seen the error of your ways."

"Yes, my Lord." This, too, was the simple truth, although even with Voldemort safely out of his mind, Severus wouldn't let himself risk visiting the more complicated truth: that the error of his ways had been deciding to do anything for anyone other than himself.

He was still committed to working against Voldemort, against the Death Eaters. But he was not working for Dumbledore or for Lily's memory or for her unspeakable son's sake or for the freedom of the wizarding world.

He was working for himself - - for the chance, for the first time in his life, to live in servitude to no one. Not his parents, not Voldemort, not Dumbledore, not Lily. He was working for the chance to live for himself alone.

That he probably would not live at all was another truth he did not deny. But at least he would get to decide what he was willing to die for.

Voldemort was speaking again. "What you felt for the Mudblood was desire only. You wanted her. I understand that. Boys want such things - - physical pleasure with women. It's natural," he said, in a tone that suggested he could think of few things more _un_natural.

Here, at least, appeared to be something that hadn't changed during the Dark Lord's exile: for as long as Severus had known him, Voldemort had always been disgusted by sex, by the animal impulses that drove lesser beings.

"Natural," Voldemort said again, his nostril holes flaring in distaste. "And did I not tell you at the time that you would find other women, pureblood women, who were worthy of you? Or at the very least, a halfblood of good family, one whose touch would not defile you?"

"You did, my lord."

"And you have known such a half-blood carnally, haven't you?"

Though he wasn't sure he liked this turn in the conversation, Severus didn't have to wonder how to respond; this was a question to which Voldemort likely already knew the answer. "Yes, I have," he said.

His first sexual experience, not long after he'd left Hogwarts, had been with someone to whom Lucius Malfoy had introduced him, a genteel half-blood girl called Elda. "Someone suitable, one of our kind," Lucius had said, and Severus had taken it as a given that the Dark Lord knew of the whole situation.

The relationship, if such it had been, hadn't lasted, of course. Elda had fairly quickly moved on, for reasons Severus no longer remembered. Since then, there had been a few meaningless others - - mostly Muggle women he'd met during the summers in the pubs of Spinner's End. But he'd kept the connections carefully casual, and for the past two or three years, he hadn't indulged even in one-night-stands.

So on the whole, Severus lived the life of a monk, and he no longer thought he minded.

Unfortunately, the Dark Lord was now studying him with an expression that Severus thought did not bode well for his continued celibacy, and Voldemort's next words confirmed his fears.

"Then you have sufficient experience for what I need from you. You see, Severus, there is a pureblood witch whom I wish you to bed."

~ / ~ / ~

Upon his return to Hogwarts, Severus did not report to Albus as he normally would; he merely dispatched an elf to say that all was well and that the meeting had been of no great import.

Because there was no way in hell - - not in the worst hell anyone could devise - - that Severus was going to tell Albus Dumbledore that Voldemort had ordered him to fuck Minerva.

"She is a blood traitor, but a pureblood nonetheless; thus she is worthy of you, and you of her," Voldemort had said. "And she is known to be close to Dumbledore. I must learn as much about Dumbledore's plans as I can, Severus."

"I will share - - " Severus began, but the Dark Lord interrupted.

"You will report what you are able, yes; I trust you will give me no cause to doubt that. Yet Dumbledore is wily. There is much he will not tell you."

The great snake had wound its way into Voldemort's lap at this point, and the Dark Lord had paused to stroke it, scaly hand upon scaly head. "There is much he will not tell _her_, either, of course," he had continued. "But she will know some things that you do not, and you must learn them."

"Legilimens?" Severus had suggested. Voldemort must be made to see that there were workable alternatives to bedding Minerva.

But Voldemort had shaken his head slowly from side to side, and rather unnervingly, the giant snake's head had mirrored the motion. "I know Professor McGonagall from earlier days, Severus. She is a witch of ability, however. . .misguided she might be. You would not be able to invade her mind without her knowledge. No, you must take her to bed. Get her to trust you, to need you. Let her _want_ to talk to you. Let her think she can save you. Women like that sort of thing, especially Gryffindors. She might even be foolish enough to believe she loves you."

The notion was laughable, but Severus said merely, "Perhaps she already has a lover." Minerva was private; he knew very little about her personal life.

But again the two heads had moved in negation.

"Lucius has conducted enquiries for me. She is unattached. She is not young, Severus, and she is apparently unwanted. She will be grateful to you, you'll see."

But then Voldemort had looked at him sharply, and Severus had to fight not to drop his eyes. A Dark Lord double-take was never a good sign; the best response was not to show any possible unwillingness.

"You seem reluctant, Severussss," Voldemort had said, his voice hissing audibly. Another bad sign. "What is the difficulty? Does Professor McGonagall remind you of your mother?"

Severus had barely stopped himself from snorting. "No," he said, as dryly as he dared. Eileen Prince would never have won any "mother of the year" awards, but if truth were told, she had been a better mother than he'd been a son. Minerva, on the other hand. . .well, few women struck him as less maternal, no matter that she spent her life with children. It was one of her most appealing characteristics.

"Is it her age, then? You think she is too old? Useless? She is disgusting to you, perhaps?"

Severus had known better than to fall into that trap: as best he could recall, Minerva was only a year or two older than the Dark Lord himself. Thus he couldn't offer age as a problem, and in truth, it wasn't.

Nor did he find Minerva unattractive, prim though she could be. In his student days, she'd drawn the attention of more than one hormonal boy, and a few girls, too. Severus hadn't liked her - - she was a Gryffindor, after all - - but he hadn't been unaware of her possibilities. The only time he'd ever agreed with Sirius Black was when he'd overheard the git snicker to his toady Pettigrew that McGonagall had nice tits.

Voldemort was waiting for an answer, so Severus gave it. "Not at all, my lord; she is in the prime of life. But. . .she was my teacher. And I her student. It would be difficult for either of us to consider the other as a - - "

"A minor problem, Severus. It has been many years since you were her student. You will simply have to adjust your thinking and convince her to do the same. And once you have become essential to her, you can begin to change her mind about her wrong-headed allegiance to Mudbloods. Women are easier to lead when their hearts are engaged. Just look at Bella and Narcissa."

Voldemort had slid the snake round his shoulders and stood, signaling the end of the audience.

"That's settled, then," he said. "You will begin a liaison with Professor McGonagall and bring me your first report in a month."


	2. Chapter 2

Chapter 2

~ / ~ / ~

As Severus poured a too-large portion of firewhisky into a hastily-_scourgified_ potions beaker, he was not unaware of the irony of the drink's provenance.

Minerva had given it to him one year for Christmas - - a bottle of 27-year-old MacMuir. From a small wizarding-family distillery. Rare. Expensive. Far too generous a present for one colleague to give another, and not normally one that Severus would have been willing to accept. He didn't like gifts of any sort, viewing them as no more than prepaid expectations.

But he'd understood that Minerva's offering was not a gift: it was a part of a debt, one long owed him.

She'd paid the first instalment near the end of his second year of teaching, knocking on his dungeon door a few nights before the Leaving Feast. Severus had been startled to see her: although he never actively discouraged visitors, he made little attempt to socialise with his colleagues, and they, in turn, did little to seek him out. He couldn't remember the last time anyone but Slytherin students had come to his door - - or if there had ever even been a "last time."

"Minerva," he had said, doing his best to act as if her appearance at his rooms was nothing out of the ordinary: he had an obscure sense that to show surprise would somehow give her the upper hand.

Unlike a few others, Minerva had not been overtly hostile to him when he'd joined the staff, but that could have meant only that she was better at concealing it. He certainly had no reason to trust her, not after the fraught relationship they'd had during his student days, and if she thought that showing up unexpectedly was going to wrong-foot him, he decided that she could think again.

"Severus. May I come in?"

He'd paused just long enough to let her know that this proposal was not entirely welcome, and then he stepped back to motion her inside with a gesture that she was free to interpret as ironic if she wished.

He did not invite her to sit, nor did she ask to - - and it was this restraint on her part that let him know that whatever was going on here, the upper hand at the moment was his. The Minerva of the staff room, with her quick temper and dry, often cutting wit, would have made some biting remark about Slytherin concepts of manners and taken a seat on her own. But the Minerva standing on his rather worn carpet was almost diffident, and Severus was immediately wary.

With the typical Gryffindor air he hated - - that of a martyr bravely about to mount the pyre - - she'd got directly to her point.

"Severus, I've owed you an apology for many years, and it's high time I delivered it. You were done a terrible wrong when you were a student, and I should have done something about it, but I did not."

"Just one terrible wrong? And which have you decided it is?" For the first time, he realised, he was actually speaking to her as his equal, not as his former teacher, and it was a heady feeling. He was almost eager for her to speak again, so that he could meet her straight-on.

She'd ignored his tone and simply answered the question. "I'm speaking of the incident at the Whomping Willow involving Black and Potter and Remus Lupin."

Severus gave a bark of laughter, though he'd rarely felt less amused. "You mean the 'incident' where Black thought it would be funny to watch the werewolf rip me apart? _That_ little 'incident'?"

Minerva had closed her eyes, and Severus had welcomed the chance to push her harder, though he let his voice go quiet. There was no need to shout facts as damning as these; the words themselves were loud enough. "They could have killed me, Minerva. You know they wanted to."

She'd made a small, abortive movement, as if she'd been about to touch him but then thought better of it. "Severus, I honestly did not know how serious the situation had been. I didn't find out the whole story until much later, after you'd all left Hogwarts."

Then she stopped and shook her head. "No. I will not make excuses. It is true that I didn't _know_ what had happened. But I suspected that it was something fairly significant. I suspected, and instead of finding out the truth, I let myself be persuaded that someone else knew best, that the problem would be fixed and that I could stay out of it." She paused, looking Severus straight in the eye. "It was wrong, and it was weak, and I let you pay the price for my cowardice. I'm sorry."

Severus had hardly known how to respond. She'd seemed sincere, which to his mind was a sure indication that he ought to be suspicious. Yet part of him wanted to believe her, and still another part was lit with a rage he thought he'd long mastered. "You're sorry?" he snarled. "And that's enough? You can go comfortably back to your life now?"

This time she did touch him, resting her fingers lightly on his Marked arm, and he'd forced himself not to flinch. "Not comfortably, no."

As quickly as it had flared, the anger faded, and Severus was suddenly weary. "Why are you telling me this now?"

"Mostly for your sake. In case it may help you to know that the injustice is not unrecognised."

"'Mostly_'_ for my sake?"

"And partly for my own," she said, with that characteristic honesty that Severus sometimes grudgingly admired and more often deplored. "One thinks about many things in the small hours of the morning."

Of course she did. That was another Gryffindor trait: self-flagellation as art form. Still, he'd had no immediate reason to doubt her, so Severus had found himself giving her a tight nod, accepting at least the impulse toward apology, if not yet the thing itself.

She'd taken her leave almost immediately afterward and never directly raised the subject with him again.

But a few years later, the firewhisky had been delivered to the foot of his bed by a house-elf on Christmas morning, the first and last present Minerva had ever given him. It had come with a card that read, "For the wakeful wee hours."

That's when he'd understood that he was receiving not a gift, but a payment, or rather, the symbol of it. The real payment was whatever thoughts kept vigil with Minerva in the night.

And so he had kept the bottle, not as a gesture of forgiveness - - he honestly had never understood what that word meant - - but as an indication that he was willing to let them be on an equal footing with each other. That he was willing to give up the advantage over her that he had gained from her failure in the matter of Potter and Black.

It wasn't a position he yielded lightly; he didn't have so many advantages that he could afford to lose one.

So perhaps it had been a sort of forgiveness after all.

~ / ~ / ~

Severus had had the MacMuir now for nearly ten years; he was as abstemious with alcohol as with sex. If he'd learnt nothing else since Lily's death, he'd learnt the dangers of giving up control. Yet sometimes, nothing but chemical oblivion would do.

Not that he intended to drink enough to pass out. But a little dulling-of-sensation wouldn't come amiss.

The trouble was, he wasn't sure exactly what sensation he was trying to blunt: the surreal strangeness of being whored out by Voldemort? Or the fact that he could now admit to himself that the thought of sex with Minerva had its appeal?

Things had been different between them after the night she'd offered her apology. Despite Severus's initial inclination to dismiss her words as too little, too late, he'd felt more comfortable with her as time went on: there was something about having seen your enemy's soft underside that made life a little less difficult.

Except that somewhere along the line, he had ceased to think of Minerva as an enemy. If he wouldn't have gone so far as to call her a friend, at least he saw her as a fellow inmate in the prison and no longer as one of the Dementor guards. They'd even taken the odd drink together over the years, although he'd never offered her the MacMuir: they'd already said enough to each other with that.

He certainly saw her as a worthy opponent, one he thoroughly enjoyed besting, in large part because she never made things easy for him. Severus had come to believe that her competitiveness was a mark of her respect.

And perhaps of something more. Something like attraction. He'd sometimes felt it himself, and there had been times that he'd been sure she felt it, too. Usually, though, he did his best to dismiss these ideas as absurd. Why would Minerva think of him as anything other than a former student - - a surly, difficult one at that - - and why would he want her to?

Yet mutual attraction did help explain the undercurrents he felt in their unending attempts to get a leg up on one another. So to speak.

She'd started the one-upsmanship; there was no question about that. He remembered the day it began in earnest. They'd been in the staffroom one afternoon during Severus's fourth year of teaching, and Madam Hooch had been congratulating a beaming Pomona Sprout on Hufflepuff's current lead in the term's Quidditch standings. . .

~ / ~ / ~

"Do you know," Sprout had bubbled in her exasperatingly irrepressible way, "I think this just might be the year that Hufflepuff actually wins the Quidditch Cup! Wouldn't that be a treat for the badger-kins? Poor things, they've had rather a drought these last few years when it comes to awards." Her gaze moved down the table to Severus, and although he'd averted his eyes, he hadn't been quick enough.

"A small wager, perhaps, Severus?" Pomona said, smiling at him teasingly. "Slytherin is not so far behind us, you know. A little incentive - - "

Severus hadn't smiled back. "If your students need incentive, Pomona, then I suggest you spend your money finding ways to encourage your 'badger-kins' to surge ahead in the potions standings. Currently they are dead last."

"One hundred galleons says Slytherin finishes behind Hufflepuff on the potions exam, Severus." Minerva had risen from a chair near the fire, startling them all; they'd forgotten she was there.

"One hundred. . .!" gasped Pomona, and even the ghost of Binns stirred himself to mutter, "Oh, I say. . ."

Minerva stared at Severus, her eyes alive with amusement and challenge. . .and something that he'd later thought was a glint of sexual interest. "I know you'd never compromise the honour of Slytherin House by anything less than the most scrupulously fair marking, of course," she'd continued. "Are we agreed, then, Professor Snape? One hundred galleons?"

He'd stared back, knowing that more was at stake here than a mere bet, however exorbitant. Finally he nodded. "One hundred galleons, Professor McGonagall."

It was a sum he could ill afford to lose, at least not in terms of money. But in other terms, he felt, the cost of _not _wagering would have been far higher. Even then, with everything unspoken and unacknowledged, he hadn't been willing to close any doors.

As it happened, it was Minerva who lost the one hundred galleons. She'd refused his offer to let her proctor his examinations or to inspect the results, and he couldn't decide whether to feel vindicated or insulted that she thought she knew him well enough to be sure he wouldn't cheat.

She had come to his dungeons herself to deliver his prize. "Your winnings, Severus," she'd said, handing him a satisfyingly-heavy bag of coins. "Try to keep them safe. If you can, that is."

"You plan to burgle my rooms?" he'd enquired dryly.

"I plan to win them back."

~ / ~ / ~

She had, of course - - had won and lost them several times over the ensuing years, and the rivalry between Professors McGonagall and Snape became an accepted part of the lore of Gryffindor and Slytherin.

And now the combination of firewhisky and Voldemort was forcing Severus to own up to the fact that he and Minerva had used the House rivalry to conceal their sexual spark. They'd carefully channeled it into competition and edgy banter, but it was there, and if truth were told, it had grown a bit with every contest, ignore it though they would. That Minerva had been content to leave the spark unfanned was obvious, but Severus thought it might not take much to bring it to flame.

He was starting to feel the fire himself. He took a few more swallows of whisky, yet he knew it wasn't just drink that was giving him visions of how Minerva's hair might look spread across his sheets, or better yet, twisted round his fist. Of how one of those still-nice tits might fit into in his hand, or how good it might feel to pin her beneath him. He could even feel her little cat paws patting his back, see her tail switching, hear her voice purring, "twenty points to Slytherin. . . . . ."

A splash of wetness in his lap pulled him back to wakefulness; he'd nodded off and tipped his whisky onto his crotch.

Severus swore roundly before charming himself dry, but at least the shock had put paid to his burgeoning erection. Far better than having to deal with it himself.

Unlike his ever-horny dorm-mates, Severus had never liked wanking, not even as a teenager; the stickiness and indignity put him off. He took care of his needs when driven to it, and he'd mastered the cleansing charms quickly, but if he was going to have sex, he preferred it to be with an actual person: it seemed cleaner, more the way things were supposed to be.

Which brought him back to Minerva, who was very definitely an actual person. And back to the Dark Lord's ludicrous plan for her. Madness. Even if Severus had wanted to bring her over to Voldemort's side, it was ridiculous to think that Minerva could be sexually and emotionally seduced into betraying a cause she'd worked for nearly all her adult life, a cause to which she had sacrificed friends and family. Far easier just to try to _Imperius_ her.

But of course, Severus wasn't working for Voldemort, which made things easier in some ways. He could simply go to Minerva and explain what the Dark Lord wanted. It wouldn't be the world's easiest conversation, perhaps, but between the two of them, they could come up with ways to plant false sexual memories for Voldemort to read, or use the premise of romance as a ruse to funnel him misleading information.

It was a reasonable plan, but. . .god, what if Minerva, being the damned Gryffindor martyr that she was, insisted on sleeping with him as her contribution to the war effort? Severus could just imagine her stripping nobly off, her face aglow with the glory of being the Heroic Strumpet, or whatever-the-hell word she'd use, whoring herself for the Greater Good. She'd probably even get off on the idea.

The very thought of such a scenario made Severus's whisky-laden stomach roil. No. He was not going to tell Minerva a damned thing about the Dark Lord's orders. If she was going to come to his bed, she wasn't going to do it as part of some perverse grand sacrifice. She was going to do it because she wanted him. Wanted _him_: the Slytherin. The Greasy Git. The Death Eater.

He didn't even care if she also saw it as part of their unending competition.

What mattered was that in the end, she would do it because she wanted Severus Snape.


	3. Chapter 3

Chapter Three

~ / ~ / ~

Severus downed a sobriety potion before he went to bed; there was no point in waiting for the pounding head and churning gut of the morning-after.

Thus he felt reasonably good when he awoke the next day, except for the little matter of being expected to seduce a long-standing colleague who was twice his age and who had been his teacher. On the other hand, she was a colleague who didn't appear to hate him and who even seemed occasionally to feel a touch of lust for him. So part of the battle, at least, might already be won.

And with that sense of distance from himself that had become noticeably more pronounced since Voldemort's return, Severus was interested to note that even in the firewhisky-free light of day, he continued to find the idea of sex with Minerva to be something he was not unwilling to consider. On the contrary, in fact: he found he was more than willing.

He preferred to meet the Dark Lord's demands when he could, as a store of good faith against those times when he was going to fail to meet them. But rarely did doing a madman's bidding offer the opportunity for personal pleasure as well. Or for besting Minerva.

Severus left his quarters feeling less oppressed than he had in months. The axe of Voldemort's return had fallen, so one way or another (or one metaphor or another), that die was cast. And today, thank any deity ever imagined, the students would be leaving by noon. Leaving for two solid months. As soon as they were gone, and he'd done his final round of checking dorms and common room, he could turn his attention to Minerva.

He was almost looking forward to devising a plan, and he couldn't recall the last time he'd looked forward to much beyond sleep or the end of the term. Or, of course, oblivion.

At breakfast, Severus sat next to Minerva and took the opportunity, once she was engaged in conversation with Sinistra, to cast an eye over her without being obvious about it. It had been a while since he'd studied her; somehow one ceased to look carefully at people one met every day.

But he saw nothing very different from what he'd always seen: a dark-haired woman in neat robes with a figure just on the edge of too angular, a firm jaw just on the edge of too sharp, a pair of be-spectacled grey eyes that were most definitely too sharp. And nice tits.

He thought he probably should insert himself into her discussion, but before he could find a suitable opening, the meal was over. Breakfast on leaving day was always a rushed affair, and what with the inevitable last-minute scramble to get all the dunderheads to the train on time, he saw little of Minerva until evening.

But the dinner hour didn't offer Severus much chance to put a plan into action, even if he'd managed to come up with one. Though he made a point of sitting next to Minerva again, she seemed distracted and unresponsive to conversation. Not that he was very effective at trying to start any: he hadn't realised until now just how often it was she who began their banter.

He persevered over the next few days, however, and soon she was behaving more as usual, seeming to enjoy sparring with him. The time had come, he decided, to suggest a private drink.

But then Fate stepped in, as it so often did, in the form of Albus Dumbledore.

~ / ~ / ~

The day had passed quietly, and evening found Severus and his colleagues at dinner - - or more precisely, at the pre-dinner drinks gathering that Albus liked to host once term was over. The relief of not having to take his meals at the high table in a hall full of rowdy adolescents almost made Severus not mind the forced collegiality of the drinks hour. Still, he'd have skipped it, if Albus hadn't insisted on his attendance - - insisted with much geniality and twinkling, of course, but insisted all the same.

Severus was not unhappy about that insistence now, since it gave him an excuse for social interaction with Minerva. But before he could even check to see if she had arrived, Pomona latched on to him, chatting away as he reached for one of the floating sherry glasses.

"I love having dinner in this small dining room, don't you?" she asked. He was sorry to see that her usual chirpiness was beginning to reassert itself; she'd been rather nicely subdued since Diggory's death. "It's so cosy, and I think we all need a little coziness right now."

"I think a 'c' word is quite appropriate, yes, but 'cosy' isn't the one that comes to mind," Severus replied.

"Yes, Pomona, you know Severus," said Minerva, joining them. "He's probably thinking of '_crucio_' - - as in wishing he could use it to fell the lot of us."

"I was thinking of 'claustrophobic,' actually. But your idea is not without merit."

"Oh, you two," said Pomona, slapping Severus lightly on the arm. "You don't fool any of us, you know, with this mutual-animosity routine. You wouldn't know what to do without each other."

Minerva treated Severus to a lightly-raised eyebrow and a half-smile; she hadn't missed his pained expression at having to endure Pomona's touch. He waited for her to harass him further, and she didn't disappoint. "Is that true, Severus? You wouldn't know what to do without me?"

If he wanted to, Severus thought, he could easily interpret this remark as flirtatious; then again, maybe he was just projecting. Still, as he offered a tiny smirk in return, he entertained himself by imagining what she might do if he flirted back with the sort of line that cretins like Black and Potter would have thought irresistible: 'I could think of a few things to do _with_ you.'

Instead he said, "I wouldn't know what to do without the galleons I so frequently win from you in your impetuous wagers."

Pomona laughed, shaking her head. "Incorrigible, the both of you. Well, I'll leave you to it, my dears. Enjoy yourselves." And off she wandered.

Minerva said something dry in response that was no doubt intended to chastise him, but Severus didn't listen; he was considering how best to offer his drinks invitation. So intent was he that he missed the approach of the Headmaster until Dumbledore spoke nearly in his ear.

Fuck. Five minutes' attention to seduction, and already he was forgetting to watch his back.

"Ah, Minerva, Severus," Albus said, in a plummy tone that immediately told Severus they were going to be imposed upon. "I wonder if the two of you might have an evening free this week. After dinner tonight, perhaps? If you could spare me a few moments?"

He clearly didn't expect them to say no, and they didn't. Minerva said merely, "Your office?" and Albus nodded.

"If you would be so kind."

If we would have a choice, Severus thought. But of course didn't say.

~ / ~ / ~

"Thank you for giving me your time," Dumbledore said later as he waved them to chairs in front of his blazing office hearth. Summer it might be, but the castle held on to the cold as if it letting it go would mean it might never return.

"Brandy?" Dumbledore asked. "No, thank you," Severus said; unlike Voldemort's, Albus's hospitality could be safely turned down. Minerva just shook her head. She seemed calm as she took her seat, though when Albus started speaking, her fingers began to pleat and unpleat a section of her robe.

Severus sat as still as he could and raised a set of light Occlumency shields. Dumbledore was always scrupulous about not entering Severus's mind without permission, but then again, the Headmaster had proven time and again to have powers that surpassed the ordinary. The ability to follow other people's thoughts without their knowledge might well be one of them.

"We've received our first reports from the Order," Dumbledore told them. "They've been interviewing Muggles and magic folk alike to see if we can track down Death Eater activity, look for patterns. We need to check the results as soon as possible, and there's a great deal of intelligence to sift through."

He Levitated a small wooden chest over to them. Severus took it on his lap, since Minerva made no move to touch it. Inside were a number of crystal phials with tiny labels that became large and readable as Severus ran a finger over them: "Malcolm Davies, 54, Horton-on-Wye, June 4, 1995"; "Melissa Grundy, 26, Weybridge, June 6, 1995," and at least a dozen more.

"Now that term is over," Dumbledore went on, "I'd like the two of you to coordinate the various Order reports. Severus, you won't want to know too much detail, of course, but we'll need to decide what information you should tell Voldemort. And it will be useful to know what he's keeping from you. He obviously won't tell you everything, but our own surveillance will help us figure out just what he's concealing.

"The phials contain memories that we hope might be revealing. I thought perhaps you could look at a few of them tonight."

Minerva's fist clenched, and Dumbledore raised a hand to forestall her speaking. "Yes, many of them were taken from Muggles without their knowledge before they were Obliviated. I know you don't approve, Minerva, and I don't disagree, but those scruples are ones we can't afford just now. There's too much we need to know. Will you look at the samples?"

There was a pause before Minerva answered, "You know I will," and it occurred to Severus that she might feel very much as he did when given orders by Voldemort. True, the Dark Lord rarely phrased his demands as questions, but that was beside the point.

"Excellent," said Albus, rising. Severus lifted the chest of memories as Dumbledore handed Minerva another square wooden box, saying, "I've shrunk my Pensieve for you. Now, I may have to leave the castle for a day or two, but when I return, we can make plans for the rest of the summer. With luck, we might even manage a week for a holiday."

~ / ~ / ~

At the bottom of Dumbledore's staircase, Minerva and Severus turned without comment in the direction of Severus's office; somehow the dungeons seemed a suitable place to examine the memories.

Severus had no feelings one way or another regarding the ethics of what they were about to do. Of course it was invasive, but it was by no means the worst of what was to come once war began again, and he had learnt not to dwell on actions that didn't end in torture or death.

Beside him, Minerva stalked silently, carrying the Pensieve, and when they reached Severus's office, she thumped the box in the middle of his desk.

He snorted. "Before you start dumping things left and right, you might at least make sure you're not crushing anything valuable."

"Och, man, if you're daft enough to leave valuable, crushable things sitting on your desk, you deserve the loss."

Severus refrained from rolling his eyes. Not the brogue already. It too often heralded that touchy mood Minerva had been exhibiting more and more of late. She sometimes followed the irritation with a recklessness of word or wager that had benefitted Severus more than once. But he hoped she'd control herself tonight; they had a lot to do.

"Just levitate it over here," he said, using his wand to shift some books and parchments from a small table onto the floor.

Minerva began unpacking the memory phials as soon as they'd restored the Pensieve to working order. "Let's get started," she said. "We might be able to get through half of them tonight."

After three hours, though, they had looked at only about a third of the memories. Some were almost comical; most were tedious; a few made Severus struggle not to look away. Wizard and Muggle alike, most people appeared to lead lives that were limited and narrow, spent with other people they often didn't seem to like. There were some moments of pleasure, of tenderness, of something that might pass for joy, but even those memories were painful to watch, given that they frequently ended in some DE-related misery.

Severus spent the three hours side-by-side with Minerva; like him, she resolutely watched every moment of every memory, no matter how bad. Severus became adept at reading her responses: the indrawn breaths of shock, the entwined fingers of sorrow, the sudden slight jerks of her head that meant she'd seen something she wanted to turn away from. Once she reached out to grip his arm, and he didn't pull away, but after a few moments she dropped her hand.

It occurred to him briefly that he should have offered some comfort, taken the chance to get closer to her, but then he dismissed the notion. There was no comfort to give, and had there been, it was not the sort of thing to come from him. Better just to bear whatever had to be borne.

Finally, sometime after midnight, they came out of a rather frustrating, inconclusive memory that may have been a Death Eater-arranged ambush or may have been just an unfortunate lorry accident.

"Enough, Severus," Minerva said as Pensieve images faded. "I've done for tonight." She rested her fingers on the sides of her head, massaging her temples briefly and dislodging a lock of hair.

With that increasingly-common sense of detachment, Severus wondered what she would do if he reached over to tuck the strands back into place. Or if he let his fingers trace her jaw.

Or if he stepped up behind her and let her feel the erection that had been growing steadily as he'd watched both the memories and Minerva, noting the rise and fall of her breasts, the sheen of her hair, the warmth of her body whenever a cramped memory space forced them close together.

What would she do, if he touched her?

Minerva leant over the Pensieve to give the swirling contents a stir before gathering them into the phial, and Severus found himself moving to her, resting his hands on her shoulders, still with that sense of merely watching, of observing, the way they had been doing for so long tonight.

She stiffened at his touch, but otherwise didn't move. Nor did she move when he let his thumb stroke the skin above her collar or let his hands trail down her arms. And when he bent forward just enough to let her sense the hard outline of his cock against her, he thought that she leant equally lightly back into him.

"It will change things, Severus," she said quietly.

"So does watching other people's unhappiness," he replied, nodding towards the Pensieve and sliding his hands around her waist.

He could feel her breathing quicken, and he moved closer behind her. It was like a dance, or what he imagined a dance must be, a choreographed give-and-take, and he was leading. Her very breath was in his control. He liked that.

Minerva dipped her head to acknowledge his words. "Very little is as it once was," she agreed. And still did not move away.

Keeping his hands on her waist, Severus stretched up his thumbs, letting them brush the bottoms of her breasts, and the feel of the smooth curves, coupled with the sound of her sharp inhalation, made his cock jump. He tightened his grip and pushed a little harder against her; he intended to give no quarter.

This time, she definitely leant back into him, pressing his length between them; then she put her hands on his and moved them to cover her breasts.

The sensation was almost overwhelming. He would have thought it impossible for his cock to stiffen further, but he would have been wrong.

To regain his lead, he stepped away from her, breaking all contact, and she turned, surprised. Over her shoulder, he could see the silvery memories still glinting in the Pensieve, and further to the rear of the room was the space that marked the hidden door from his office to his quarters.

"My rooms," he said, somehow finding his wand and unmasking the door. "I'll be in the bedroom. Come to me there, if you choose to. And take your hair down."

Then he strode off, not looking back at her, enjoying the chance that she'd hear "come" as a play on words, enjoying even the little frisson of doubt as to whether she would follow. Would she take such orders from him? He thought she might, but. . . . He'd soon see. And if she did. . .

Well. The game would be his.


	4. Chapter 4

Chapter 4

~ / ~ / ~

Severus had his back to the bedroom door when he heard Minerva step inside, and he waited for her to cross to him, not moving until he felt a light hand on his arm.

When he finally turned to her, he saw first that she'd removed her glasses, and then that she'd actually done as he'd asked: she'd let her hair down to fall over her shoulders, long and straight and silvery-black.

It was the first time he'd ever seen it loose, and the thought of how it would look brushing against her bare breasts was enough to make him abandon his vague plans for lengthy foreplay. Instead, he pulled her towards his bed, opening his robes as he went.

~ / ~ / ~

Once she lay naked before him, he realised that her skin was nearly as pale as his own; she would probably bruise easily, the way he did. The idea wasn't displeasing to Severus, and he bent over her, tracing his lips along her collarbone and then nipping sharply at her neck.

She cried out, and he felt her legs open under him. A flush of triumph surged through him.

"Desperate for it, are we, Minerva?" he whispered, squeezing her breast, which filled his hand as nicely as his fantasies had suggested. In answer, _her _hand went straight to his erection and closed tightly around it, taking him just to the exhilarating edge of pain before she eased off. She knew exactly when to stop, and it occurred to him briefly that Minerva's past might be more interesting than he'd ever suspected.

Then there was no more space for thought as she began stroking him, softly at first, and then harder, the fingers of one hand wrapped hotly round him, the thumb of the other brushing lightly over the head of his cock.

He tried to bite back his groan of pleasure, but failed, and she chuckled. "Desperate, are we, Severus?"

He snorted with what he hoped was sufficient disdain, but inside he relaxed a bit. This was a game he knew well: one way or another, it was the one he and Minerva had played for years. Back and forth, one up, one down - - that was his relationship with her in daily life, and as far as he was concerned, it made for a fine dynamic in bed, too.

With a sound that even he wasn't sure whether he'd call a snarl or a laugh, he leant back to balance himself and then took hard hold of her, pulling her hands off him, muttering a charm that pinned her wrists to the bed. She was at his mercy.

But he'd reckoned without Minerva's abilities with wandless magic. Suddenly he was frozen in place, and tantalizing prickles of heat and cold - - he could scarcely tell which - - began to trail down his back and then around to his abdomen, the touch feather-light and highly arousing. She was the one in control now. He couldn't move, his cock was throbbing, it was almost too much. . .and then just as suddenly as the sensation had started, it stopped. Either Minerva couldn't maintain the spell for long without her wand, or else she didn't want to wait any more than he did.

Whichever, it didn't matter. Severus was ready. As soon as he could move again, he levered himself over Minerva and entered her swiftly. It felt good - - glorious, in fact - - but not so overwhelming that he missed the satisfying way he'd made her gasp and arch beneath him.

He paused, motionless, until she wrapped her legs around him and lifted her hips, which was probably as close to begging as she'd ever bring herself. Only then did he release her hands and begin to move.

~ / ~ / ~

Severus awoke to a thin, grey dawn and the unaccustomed heat of another person in his bed. He lay still for a moment, feeling nothing in particular, certainly none of the awkwardness he might have expected, given that he'd spent the night having sex with a woman older than his mother, a woman he'd once thought he disliked and who could still thoroughly unsettle him.

Things will change, Minerva had said, and of course it was true. Change was something Severus knew well. Lily Evans had once been his life, and now she was little more than his convenient shield against the world. Albus Dumbledore had once been his saviour, and now he seemed just another demanding master. Lord Voldemort had once been dead, and now he was alive.

What could any new change matter after those?

He turned to look at Minerva. She slept on her side, facing him, her expression as stern in sleep as it was in waking. At some point, she'd thrown off the blankets, and now he took the opportunity to appraise her body as he had not been able to do the night before, what with the dim candlelight and the bedclothes and his own driving need.

She was old, the Dark Lord had said, but Severus's experiences with the naked young were not so numerous that he had much to compare her to. Her skin might be a little less taut, her breasts a little less firm than had been true of his other few bedmates, but she had felt the same - - wet and warm, a potent combination of soft and tight, her lips smooth on his chest, her nails sharp on his back.

He had no complaints.

And if she were to conduct a similar appraisal, what would she think of him? He knew what she would see: a man pale, lean, and bony, his chest only sparsely-haired, his feet absurdly narrow, with that long second digit his mother had called "the Snape toe." "A toe like a finger," she'd say, and Severus had always felt its oddity.

Well, Minerva hadn't seemed to object to him when she'd been lying underneath him, urging him on with her hands on his arse. He'd not been particularly gentle with her, but she hadn't seemed to want him to be. Nor had she been gentle in return; she'd met him thrust for thrust with an intensity that he'd liked and supposed he should have expected. Minerva was fierce and hard and demanding in everyday life; why should she be any different in bed?

He touched her throat lightly, grazing the mark he'd left there; he wondered if she'd keep it.

And he wondered if she would be willing to continue sleeping with him, for the summer, at least. The Dark Lord would expect the relationship to continue, and Severus admitted to himself that he wouldn't mind it, either. No strings, of course. . .but an affair could help them both pass a time that always felt out-of-joint to Severus, outside of real life. Especially now.

What might happen when the summer ended, he didn't let himself consider. With the Dark Lord back, he saw no point in planning much of a future.

But for the short-term. . .

For the short term, maybe he could share his bed with Minerva. If she wanted to. If the idea didn't repulse her. Maybe they could even manage to keep the liaison a secret from Dumbledore.

He found himself anticipating their next encounter. They could take things slowly, could tease and tantalise and test each other. They could even kiss, something he didn't think they had done, this time. They could. . .

Next to him, Minerva stirred and turned over, curling in on herself. She might be cold, Severus thought; his room was chilly. He considered drawing her into his arms, spooning behind her and warming her, but he didn't.

Instead, he drew his old quilt over both of them. Then he settled on his side, his back to Minerva, and let sleep take him once more.

~~fin

**A/N** - - And here "Mutability" ends. I hope this final chapter isn't too disappointing for those of you who prefer more closure, but like Samuel Johnson in _Rasselas_, I often write "conclusions in which nothing is concluded." I like stories that are ambiguous or open-ended.

But I can promise you that I'll be writing about Severus and Minerva again; I find that I'm not yet finished with them.

My grateful thanks to all my readers and especially to those of you who have sent me such kind and welcome reviews. I'm always so pleased to hear from you.


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